But Deandre got criticized for changing his mind. Shouldn't Danny get criticized if he does the same thing?
He's not changing his mind. He is just keeping a tentative agreement tentative. He has too much character to go back on his word, hence why he stuck to his draft promise to JR Giddens even when, ironically, DeAndre Jordan unexpectedly was still available.
My suspicion is that he is trying to figure out if he can still use Pressey's unguaranteed contract for something before July 15. If he can, then Babb is sent to Golden State as the necessary salary in the Lee-Wallace deal. If not, then Pressey gets sent and Ainge still has Babb's contract to use in a deal. He could just send Pressey now, but someone might actually want Pressey, so why make the deal before you explore all options?
It can be something small like Pressey for a minimum salary veteran third-string big-body center who can be used to provided mediocre but credible defense against bigger centers.